Through-tubing bridge plug having covered expansible packer

ABSTRACT

Method and apparatus for emplacing a bridge plug through tubing in a well penetrating subterranean formations characterized by the following plurality of steps, without requiring removal of the tubing. A covered expansible centralizer, packer and dogs are run downwardly through tubing to a predetermined depth. The dogs are released for holding against the casing. The cover tube is lifted from around the expansible centralizer, packer and additional dogs, allowing the packer to expand outwardly into contact with the casing. The cover tube and the dog release are removed from the well. A predetermined amount of sand is dumped onto the expanded packer. A predetermined batch of cement slurry is dumped onto the top of the sand. An open passageway is provided through the sand and the cement slurry during curing. After the cement is set, the open passageway is closed. Finally, if desired additional cement slurry is dumped onto the set bridge plug and allowed to set. Also disclosed are the specific and preferred structural forms of the various means for carrying out the functions implicit in the steps; for example, the vent plug located at the top of the vent tube; the upwardly and downwardly opening pair of packers; and the &#39;&#39;&#39;&#39;tattle-tail&#39;&#39;&#39;&#39; for showing that the open passageway has been closed satisfactorily.

United States Patent 1191 Owen et a1.

1 1 June 24, 1975 1 1 THROUGH-TUBING BRIDGE PLUG HAVING COVERED EXPANSIBLE PACKER [75] Inventors: Harrold D. Owen; Jamie B. Terrell,

both of Fort Worth, Tex.

[73] Assignee: Gearhart-Owen Industries, Inc.,

Fort Worth, Tex.

22 Filed: Jan. 8, 1974 211 App]. No.2 431,711

[52] US. Cl. 166/285; 166/133; 166/182;

166/202 [51] Int. Cl. E2lb 33/00; E21b 23/00; EZlb 33/12 [58] Field of Search 166/285, 286, 133, 162,

[56] References Cited UNITED STATES PATENTS 2,618,344 11/1952 Turechek et a1 166/63 2,672,200 3/1954 Patterson 166/202 2,969,839 [/1961 Greene 166/162 2,978,029 4/1961 OReilly et a1. 166/123 3.431974 3/1969 Buck et a1 166/202 3,489,216 1/1970 Armstrong ct a1 166/135 3,623,550 11/1971 de Lajorte 166/202 Primarv Examinerlames A. Leppink Attorney, Agent, or Firm-Wm. T. Wofford 5 7 ABSTRACT Method and apparatus for emplacing a bridge plug through tubing in a well penetrating subterranean formations characterized by the following plurality of steps, without requiring removal of the tubing. A covered expansible centralizer, packer and dogs are run downwardly through tubing to a predetermined depth. The dogs are released for holding against the casing. The cover tube is lifted from around the expansible centralizer, packer and additional dogs, allowing the packer to expand outwardly into contact with the casing. The cover tube and the dog release are removed from the well. A predetermined amount of sand is dumped onto the expanded packer. A predetermined batch of cement slurry is dumped onto the top of the sand. An open passageway is provided through the sand and the cement slurry during curing. After the cement is set, the open passageway is closed. Finally, if desired additional cement slurry is dumped onto the set bridge plug and allowed to set. Also disclosed are the specific and preferred structural forms of the various means for carrying out the functions implicit in the steps; for example, the vent plug located at the top of the vent tube; the upwardly and downwardly opening pair of packers; and the tattle-tail for showing that the open passageway has been closed satisfactorily.

25 Claims, 18 Drawing Figures SHEET PATENTEIJJUN 24 1915 PATENTEDJLIN 24 ms SHEET fiiyza E925 PATENTED JUN 2 4 ms SHEET PATENTED JUN 24 I915 I saw 1 THROUGH-TUBING BRIDGE PLUG HAVING COVERED EXPANSIBLE PACKER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to sub-surface well apparatus; and, more particularly, to method and apparatus for setting a bridge plug or the like in a wellbore penetrating subterranean formations and having tubing therewithin.

2. Description of the Prior Art The need for bridge plugs in wellbores penetrating subterranean formations is well known; particularly in oil-or gas-producing wells. For example, it frequently happens that there is more than one zone, or formation, of production that is to be produced independently of each other or wells in which it may be desirable to seal off lower producing zones for one or more reasons. Emplacement of bridge plugs does not present a particularly difficult problem during the finishing of a well and before tubing has been emplaced thereinto. When it is desired to place a bridge plug in a wellbore after tubing has been inserted into a well, however, the prior art devices have not produced totally satisfactory method and apparatus for setting the bridge plug through the tubing. Consequently, operators of such wells with tubing have ordinarily resorted to pulling the tubing. In our co-pending application Ser. No. 353,969, entitled Through-Tubing Bridge Plug, we described an improved method and apparatus that alleviated many of the difficulties of the prior art and provided features that had not been provided theretofore. This invention comprises a further refinement and improvement in the method and apparatus described in the aforementioned Ser. No. 353,969, the descriptive matter of which is incorporated hereinto by reference. In addition, our experience in building through-tubing bridge plugs has indicated the following features are desirable and have not been provided heretofore;

l. A bridge plug employing set cement is a preferable permanent type of bridge plug and an open passageway should be provided for venting pressure or continuing production while the cement slurry is curing, or setting. The apparatus for effecting the set cement should have characteristics that will provide for the set cement the best strength and other physical properties that is possible. The apparatus should provide the largest possible vent, or open passageway, through the cement while the cement is setting.

2. The vent plug should be moved to a closed position by well pressure in order to have a large force without requiring expensive well tools capable of generating the large force.

3. The vent plug must be locked in its closed position by means that are immovable longitudinally of the vent tube.

4. The vent plug should be movable into its closed position at any desired time, rather than requiring a certain time with respect to the setting, or curing, of the cement.

5. The vent plug should be located at the top portion of the vent tube above the upper vent apertures for a plurality of reasons; for example, (a) the location at the top allows the vent tube to have a larger inside diameter for flow of fluids therethrough than if controls have to be disposed therewithin; (b) the cement will have less tendency to settle onto the valve; and (c) it facilitates connection of a tattle-tail that can be freed if the vent plug is closed satisfactorily.

6. The apparatus should provide a tattle-tail that will demonstrate to the operator at the surface that the vent plug has been closed satisfactorily.

7. The apparatus should provide a packer that has at least an upwardly looking, or open, frusto-conical section for receiving sand, cement and the like with satisfactory strength to hold the cement until it sets.

8. It is also desirable that the packer have a downwardly opening frusto-conical packer section to channel fluid through the vent tube more effectively and alleviate problems with the tendency of the fluid to flow adjacent the casing and around a cement plug being set thereinto.

9. The expansible packer should include a plurality of packer leaves that are designed to have a tangential opening force by a suitably shaped fan-shaped section.

As indicated hereinbefore, the prior art has failed to provide totallyy satisfactory method and apparatus for setting a bridge plug that has the foregoing features.

Accordingly, it is an object of this invention to provide method and apparatus for setting a bridge plug in a wellbore penetrating subterranean formations and having tubing therein without pullling the tubing and having one or more of the foregoing features not heretofore provided by the prior art.

It is another object of this invention to provide method and apparatus having most or all of the foregoing features and effecting the objects delineated immediately hereinbefore.

These and other objects will become apparent from the following descriptive matter, particularly when taken in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 is a schematic elevational view of apparatus in accordance with a preferred embodiment of this invention, shown emerging from tubing within a cased wellbore.

FIGS. 2A-D are partial side elevational views, partly in section, showing, respectively, the top, upper intermediate, lower intermediate and bottom sections of the through-tubing bridge plug assembly of the embodiment of FIG. 1 in the run-in configuration.

FIGS. 3A and 3B are partial side elevational views, partly in section, showing, respectively, the top and bottom sections of the through-tubing bridge plug assembly of FIG. 1 at the initial release of the bottom dogs.

FIGS. 4B, C and D are partial side elevational views, partly in section, showing, respectively, the upper intermediate, lower intermediate and bottom sections of the through-tubing bridge plug assembly of FIG. 1 in its uncovered emplacement in the wellbore with the packer extended for reception of cement slurry.

FIG. 5 is a schematic side elevational view, partly in section, of a portion of the embodiment of FIG. 1 that is left in the well with sand emplaced on the packer and a fluid bypass.

FIG. 6 is a partial schematic side elevational view, partly in section, of the embodiment of FIG. 5 with cement slurry emplaced atop the sand on the packer, still having a fluid bypass provided therethrough.

FIG. 7 is a partial side elevational view, mostly in section, showing the subjecting of a piston to wellbore pressure for closing the vent plug.

FIG. 8 is a partial side elevational view, mostly in secmoved into its closed and locked position.

FIG. 9 is a cross sectional view taken along the lines IX-IX of FIG. 7.

FIG. 10 is a cross sectional view taken along the lines XX of FIG. 8 with the chucks of the lock means moved into their closed position locing the vent plug in place.

FIGS. 11 and 12 are side and plan views of a leaf of the packer of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to the drawings, FIG. 1 illustrates the apparatus 11 for emplacing a bridge plug in the wellbore 13 penetrating subterranean formations 15. As illustrated, the wellbore 13 contains casing 17 and tubing 19. The apparatus 11 includes well cable 21, cable head assembly 23, casing collar locator 25 and the bridge plug assembly 27.

The various types of casing 17 and tubing 19 are well known and need not be described herein. It is sufficient to note that frequently the tubing has so small an internal diameter that emplacement of a bridge plug therethrough has been impractical heretofore, so that tubing was pulled from the well in order to set the bridge plug. This expense and trouble is obviated by the apparatus 11.

The well cable 21 may comprise a conventional well cable having the usual firing wire (not shown) down its center, and an armor to serve as electrical common, or ground. The firing wire traverses the length of the cable head assembly and is connected by way of the casing collar locator with an explosive stud for releasing the dogs as described hereinafter with respect to initiating the setting of the bridge plug.

Similarly, the cable head assembly 23 is conventional and need not be described herein.

Also, the casing collar locator 25 is conventional and need not be described in detail herein. It is sufficient to note that the casing collar locator is provided for verifying when the apparatus 11 has passed out of the end of the tubing or otherwise verifying a predetermined depth useful in properly emplacing the bridge plug at a predetermined depth.

The bridge plug assembly 27 includes a dog release assembly 29 and, within a cover tube 31, a packer and vent tube assembly and a vent plug assembly. The bridge plug assembly 27 is illustrated in FIGS. 2A-D in the run-in configuration.

The dog release assembly 29 is employed primarily for one purposes. That purpose is to kick the bottom set of dogs 33, FIG. 2D, out of the bottom end of the cover tube 31. The dog release assembly 29 comprises an outer tubular portion 35 that is disposed in predetermined relationship with the cover tube 29 in the run-in configuration; and an inner portion 37 that is movable longitudinally of the outer portion and disposed concentrically therewithin. To afford motive power for pushing the inner portion 37; and, consequently, the dogs 33; with respect to the outer tubular portion 35 and the cover tube 31, a spring 39 is compressed intermediate a thrust sub 41 of a thrust tube assembly 43 and a cover adapter 45 suspending the cover tube 31.

To releasably hold the inner portion 37 in its uppermost position with spring 39 compressed, there is provided an explosive stud 47. The explosive stud 47 is screwed onto a shaft 49 of the inner portion 37 and is, in turn, held in place by stud nut 51 atop the end of chamber 53. The shaft 49 is also screwed into the thrust sub 41. The shaft 49 has suitable means, such as set screws, to prevent its becoming unscrewed from the respective threaded apertures in the respective explosive stud 47 and thrust sub 41 at the ends.

In accordance with conventional practice, the explosive stud 47 has a blasting cap 55 therewithin and the blasting cap 55 is electrically connected via conductor 57 and ground with controls at the surface (not shown) for detonation. Apertures 77 penetrate laterally through the side walls of the chamber 53 in order to vent the gaseous products formed by the detonation of the blasting cap 55 in the explosive stud 47. The top portion of the explosive stud is trapped interiorly of the lower chamber of an adapter 69 atop the chamber 53. As is well known, when the blasting cap is detonated, the explosive stud disintegrates and releases the shaft 49 in order that the spring 39 can propel the thrust tube 43 and shaft 49 downwardly for a distance of from 6 to 9 inches, thereby expelling the bottom dogs 33 from inside the cover tube 31.

More specifically, the conductor 57 penetrates through boot 59 and is connected with terminal nut 61. Terminal nut 61 is insulated from ground, such as the walls of the outer portion 35 and the armor of the cable 21; for example, by insulating washer 63, inter alia. When a casing collar locator 25 is employed, a bayonet probe 65 plugs directly into suitable electrical outlet in the bottom of the casing collar location 25 in accordance with conventional practice that does not need to be described in detail herein. It is sufficient to note that the electrical conductor is insulated from ground contact with the contact sub 67. As illustrated, a contact sub 67, an adaptor 69 housing the boot 59 and terminal nut 61, the chamber 53 and a housing 71 are connected together via illustrated mating threaded connections. Conventional details of interconnection are employed in connecting the respective elements. If desired, a protective cover can be employed over the contact sub if a casing collar locator is not employed.

To facilitate assembly, a jack 73 is screwed into the cover adapter 45 to move with the cover adapter and the cover tube; and a jack nut 75 is provided adjacent the bottom of the housing 71. Thus, the jack nut 75 can be screwed close to the cover adapter 45 to allow the shaft 49 and the explosive stud 47 to be assembled and emplaced and allow the stud out 51 to be screwed over the external threads at the top of the explosive stud 47 and facilitate assembly. Thereafter, the jack nut 75 can be rotated to force the housing 71 and the remainder of the outer tubular portion 35 away from the cover adapter 45. Since the shaft 49 and thrust tube 43 are connected with the outer portion by way of the explosive stud 47 and stud nut 51; they, too, are drawn upwardly toward the cover adapter 45, compressing the spring 39 between the cover adapter 45 and the thrust sub 41. This stores the motive power for subsequently releasing the dogs 33, as indicated hereinbefore. To transmit the force stored into the spring, the lower end of the thrust tube 43 bears against the shoulders of the retrieving sub 79 of the packer and vent tube assembly 30.

The packer and the vent tube assembly 30, FIG. 2B, is inserted within the cover tube 31 below the thrust tube 43, as indicated hereinbefore. The packer and vent tube assembly has for its primary purposes providing a centralized vent tube that is open to the flow of well fluids during curing of a cement plug; and to expand the packer outwardly into contact with the causing so as to receive cement slurry for forming a cement plug. To accomplish these purposes, the packer and vent tube assembly 30 has a plurality of centralizers 83 located near its top. The centralizers 83 may comprise a plurality of branch arms; for example, four as illustrated; that are folded within the cover tube but biased to spring outwardly as soon as the cover tube is removed. Specifically, centralizer members 84 are connected via links 85 with an expansion ring 87 that is slidable longitudinally of a central shaft portion 89. The expansion ring 87 is biased upwardly by spring 91 so as to open the centralizers 83 as soon as the cover tube 31 is removed.

A vent tube 95, FIGS. 28 and 2C, comprises a tubular member that serves as a central body to which the packer is affixed and provides an open passageway through which fluids can flow during setting of any cement slurry poured onto the upper packer. Bottom apertures 97 and top apertures 99 penetrate laterally through the wall of and communicate interiorly and exteriorly of the vent tube 95. Thus, a complete bypass, or open passageway, is formed that allows fluid to flow from beneath the bottom packer through the bottom and top packers, through any sand and cement set thereonto and back into the wellbore above the cement. In this way, fluid flow, such as for producing fluids, may continue without disrupting or adversely affecting cement that is being set into a finished cement plug. Closure of the open passageway, or bypass, will be described in more detail with respect to the vent plug assembly later hereinafter.

A packer 103, FIG. 2C, is disposed on the exterior of the vent tube 95 and is extensible radially outwardly into contact with the casing 17, as illustrated in FIG. 4C. As illustrated, the packer 103 comprises two packers 105 and 107 that are pseudo-frusto-conically shaped in their extended position. The upper packer 105 opens upwardly for receiving at least a cement slurry; and, preferably, respective columns of sand and cement slurry; dumped thereonto. The lower packer 107 opens downwardly for directing fluid flow through the bottom apertures 97 and the vent tube 95 more effectively. Each of the packers 105 and 107 comprise a plurality of inner radially and peripherally extensible fan-shaped leaves 109, such as illustrated in FIGS. 11 and 12.

Each leaf 109 contains a spring member 111 that is connected to the exterior of the vent tube 95 by appropriate means; for example, by way of brads or screws inserted through apertures 113 and 115, FIGS. 11 and 2C. The other end 117 of the spring member 111 is biased to move radially outwardly. A fan-shaped piece 119 is attached to the spring member 111, as by being bonded thereto. As illustrated, the fan-shaped piece 119 is formed of thin, flexible steel that is soldered to the end 117 to move in unison therewith as the free end 117 springs outwardly to force the outer peripheral end of the fan-shape piece 119 into contact with the casing 17. The solder that is employed is a relatively high strength solder that retains its strength of bonding even at temperatures of 400F and higher for use in hot, deep wells. The fan-shaped piece 119 is thin and flexible enough to be formed into a generally tubular shaped member that closely and conformingly fits about the vent tube and within the cover tube 31, as illustrated in FIG. 2C. Yet, the piece 119 has sufficient resiliency to snap outwardly with its outer end in substantially sealing contact with the casing 17 when the cover tube 31 is removed from around the respective packers.

To obtain effective and satisfactory operation of the packer, each leaf 109 includes an arcuate portion 121, FIG. 12, that extends from the edge opposite the spring member 111 and along the radially outermost portion of the edge; for about the outermost one-half. The arcuate portion 121 increases monotonically in lateral dimensions d from a straight line 123 tangent at the beginning of the arcuate portion. The straight line 123 is substantially aligned with the edge 125 opposite the spring member 111 before the arcuate portion begins. In this way, there is a sort of tangential force imparted that more effectively snaps the packer outwardly into its sealing contact with the casing 17.

To catch sand, cement particles and the like and improve the performance of the respective upper and lower packers 105 and 107, each has a non-waterproof bag 127 disposed over both sides of the leaves. Each bag has a large central diameter so as to expand with the packers. The bag 127 folds back over the leaves 109 and has respective cuff portions at each end that closely fit adjacent the vent tube 95. The outer cuff ends are tied with respective means, such as nylon thread, about the exterior of the vent tube 95 and attached spring members 111 to facilitate assembly. The inner cuff closely fits the exterior of the vent tube 95 interiorly of the spring members 111. The bag has walls that are permeable to water so as to allow water to seep from the cement slurry through sand emplaced immediately adjacent the bag for effecting a better set cement. The term cement, as used herein, is intended to include any suitable cementious material. The bag does not have sufficient permeability, however, to allow the water to flow therefrom such that too much water would seep from the cement and adversely affect the set cement. The bag is not permeable to flow of small sand grains and the like. If desired, a fluid impermeable bag may be employed about the lower packer 107 to ensure that the fluids are directed through the vent tube 95 rather than adjacent the casing. Flow at the casing tends to funnel through, or gas cut, any cement slurry set above the upper packer 105.

The bridge plug assembly 27 contains a vent plug assembly 129 for closing the passageway through the vent tube 95 after a cement plug has been set. The vent plug assembly 129 contains an elongate closure rod 128 that extends longitudinally, or upwardly, and serves as a portion of a tattle-tail when brought to the surface as described herein. The closure rod 128 terminates near its top end 131 in an enlarged retrieving knob 133, FIG. 2A. The retrieving knob 133 facilitates being grasped by a subsequent retrieving tool, fishing tool, or the like for being pulled upwardly to close the passageway through the vent tube 95. The closure rod 128 is releasably connected with shaft portion 89 by way of roll pins 135 through retrieving sub 79. As will become clear from the descriptive matter hereinafter, the vent plug assembly 129 has a unique interlock arrangement that prevents release of the closure rod 128 and the shaft portion 89 until the vent plug has been properly seated in the vent tube 95 to close off the passageway therethrough. Closure rod 128, knob 133, retrieving sub 79 and shaft portion 89 thus constitute a form of tattle-tail, or proof positive, that the vent tube 95 is plugged and, when returned to the surface, shows excellent evidence that the bridge plug is properly set.

The interlock is referred to herein as a closure release 137. The closure release 137 includes a plurality of balls 139 that are disposed in apertures 141 in a sleeve 143. The shaft portion 89 has an annular recessed portion 145 extending longitudinally thereof and receiving the balls 139. The balls are trapped in their respective apertures 141 intermediate the recessed portion 145 and a peripherally surrounding skirt 147. Thus, as can be seen, the shaft portion 89 can be moved upwardly a limited amount; for example, sufficiently to pull the poppet valve 149 free of the aperture and sealing seat 151 for venting well fluids interiorly of the passageway 153. The shaft portion 89 and the closure rod 128 cannot be released, however, until the skirt 147 has moved downwardly, such as will be ef fected by proper closure of the vent plug 155. As can be seen in FIG. 8, once the vent plug 155 is moved downwardly sufficiently to move the skirt 147 free of the balls 139, the balls 139 are free to move outwardly and free the shaft portion 89 for withdrawal as a complete tattle-tail. The sleeve 143 is restricted in its movement by annular lip 148 as long as the skirt 147 is emplaced. Moreover, when the skirt 147 begins to be moved downwardly the balls 139 will come in contact with the lower shoulders 157 and prevent further downward movement of the sleeve 143 until the skirt 147 frees the balls 139.

The vent plug 155 is connected via suitable means, such as threaded connection 158 with the plug shaft 159. As can be seen, the vent plug 155 is disposed above the top apertures 99 to allow fluid to flow and to bypass any cement slurry being cured to set cement in the packers disposed about the vent tube 95.

In the illustrated embodiment, the force to close the vent plug 155, or move it downwardly past the apertures 99, is provided by the differential pressure of fluid pressure in the bore hole acting against a piston that is exposed to atmospheric pressure on its other side, or end face. Specifically, a piston 161 is disposed in a chamber 163 that has been sealed at atmospheric pressure. The atmospheric chamber 163 is formed within the atmospheric sub 164, which is threadedly connected with the vent tube 95. Downward movement of the piston 161 is opposed only by atmospheric pressure in the chamber 163, as well as the usual frictional resistance of the respective seals illustrated and disposed in contact with the surfaces they slidably engage, as will be described hereinafter. Piston 161 is connected with the vent plug shaft 159. As illustrated, the piston 161 and the vent plug shaft 159 are integrally formed together. The piston 161 has seals, such as o-rings 165, that sealingly engage the piston 161 and the interior walls of the chamber 163. The piston 161 is connected, as by threaded connection 167, with a tubular shaft 169. The tubular shaft 169 carries the skirt 147 at its upper end such that the skirt 147 and the vent plug 155 move in unison. Suitable seals, such as o-rings 173, are disposed in sealing engagement with the respective shafts 169 and 159 in order to isolate wellbore pressure from the chamber 163. A pressure chamber 162 is defined atop piston 161 by threaded connection 166 between atmospheric sub 164 and chuck sub 203. Seals,

such as o-rings 171 and 1&8. seal the chamber 162 from the top.

The vent plug also has suitable seals, such as 0- rings 175, disposed peripherally around its exterior surface for sealing engagement against the interior walls 177 of the vent tube 95 for plugging flow therethrough. Thus, when plugging of the vent tube 95 is desired, following successful setting of a cement plug, the poppet valve 149 is lifted upwardly, allowing fluid to flow through the aperture, seat and seal 151, and via passageway 153, orifice and non-sealing threads into pressure chamber 162. Consequently, wellbore pressure acts against the top of the piston 161. The piston 161 moves downwardly within the chamber 163 which is only at atmospheric pressure. initially at least. The atmospheric pressure inside the chamber 163 will increase as it is compressed into a smaller volume to resist too much movement of the piston 161 downwardly and to cushion what would otherwise be a shock of terminating movement. The piston 161 and the vent plug 155 move downwardly until the vent plug 155 is past the top apertures 99 and sealingly seated within the interior walls 177 of the vent tube 95. This amount of longitudinal movement is sufficient to move the skirt 147 downwardly and free the balls 139, as illustrated in FIG. 8. Thereafter, the closure rod and shaft portion 89 can be pulled from the well to indicate a successfully closed vent plug.

As will be appreciated, it is necessary to lock the vent plug into its lower and sealing position against the force created by fluid pressure from below or from above. The lock means for locking the closed vent plug in its closed position comprises a plurality of chucks 179 that are immobilized against longitudinal movement within the vent plug assembly 129 and an annular recess 181 for receiving the chucks 179 when moved into juxtaposition therewith. As can be seen more clearly in FIGS. 9 and 10, the chucks 179 are held frictionally against the shaft 169 by suitable clamping means, such as C- clamps 180. Consequently, the chucks 179 are urged to move radially interiorly and as soon as the annular recess 181 is adjacent, they will snap inwardly to immobilize the shaft 169 against longitudinal movement; consequently, immobilizing the vent plug 155 against longitudinal movement. As can be seen in FIG. 10, the chucks 179 snap into engagement with the recess 181 and are retained so by the C-clamp whose ends move more closely together. The chucks are initially emplaced within and are immobilized against longitudinal movement by the bottom 201 of the bore of the chuck sub 203 and the bottom 205 of the ball sub 207 that is threadedly connected therewith.

As indicated, the bridge plug assembly 27 also includes a dog assembly having the primary dogs 33 and the secondary dogs 187. A dog anchor 182, dog extension 183 and dog sub 184 are provided for connecting the dog assembly 185 with the packer and vent tube assembly 30. The dog assembly 185 has a central mounting ring 189 that is mounted on shaft 191, as by set screws 193. Each of the primary and secondary dogs 33 and 187 have slidably mounted expander rings that are connected to their respective dogs by illustrated pivotal linkages for expansion of the dogs outwardly once the dogs are free. The sliding movement of the expander rings 195 for expanding the dogs is effected by respective springs 197 disposed concentrically about the shaft 191 and intermediate the central mounting ring 189 and the respective expander rings 195. A typical expanded position of the respective dogs is illustrated in FIGS. 3D and 4D wherein the respective dogs have been expanded outwardly into contact with the casing 17. The dog assembly 185 is relatively conventional and further detailed description is believed unnecessary herein.

In operation, the apparatus 11 for emplacing a bridge plug in a wellbore penetrating subterranean formations is assembled illustrated and described hereinbefore with respect to FIGS. 1 and 2A-D. Ordinarily, the bridge plug assembly 27 will be about 18 feet in length. This length may vary depending upon the size tubing and easing through which and into which the plug will be lowered and set. In accordance with usual practice, care should be taken and all of the warnings observed with respect to the explosive stud employed in the inner portion 37 of the dog release assembly 29. Specifically, since the stud contains an electrically-fired blasting cap, care must be taken not to assemble the stud in the vicinity of an electric wiring, or radio emission that would generate stray currents and care should be taken to avoid striking the stud a sharp blow or creating excessive heat. Also, care should be taken to see that the springs are not compressed solidly, as by tightening the jack nut too much, which could result in damage to the explosive stud. Electrical continuity may be checked with a blasting galvanometer or other suitable instrument.

lfa lubricator is to be employed to lower the apparatus 11 into the wellbore tubing, the lubricator must be long enough to accommodate the apparatus pulse required sinker bars.

Ordinarily, it is advisable to run a gauge having the same dimensions and length as the apparatus 11 before the apparatus 11 is lowered into a well. This avoids the danger of losing the apparatus 11 to crumpled tubing, sand fills and the like. If no other gauge is available, the cover tube may be readily employed as a gauge.

Care must be exercised in running the apparatus 11 to avoid prematurly jarring the lower end of the bridge plug assembly 27; specifically, dogs 33; from the cover tube 31. Although approximately 100 pounds is required to pull the bridge plug assembly 27 from the cover tube 31, these forces can be achieved if a rapidly moving wireline is stopped suddenly. It has been found advantageous to lower the tool at a maximum rate of about 150 feet per minute and avoid sudden stops.

The apparatus 11 is lowered through the tubing 19 until it is out of the bottom end of the tubing and emplaced at the proper depth in the wellbore 13. The apparatus 11 is stopped by stopping downward movement of the well cable 21 by conventional surface equipment, such as a motorized cable drum (not shown). The explosive stud 47 is detonated, allowing expansion of the kick out spring 39, as illustrated in FIG. 3A. Expansion of the spring 39 pushes the thrust tube 43 and the packer and vent tube assembly 30 downwardly with respect to the cover tube 31, freeing the primary dogs 33 from the bottom end of the cover tube 31. The primary dogs 33 spring outwardly into engagement with the casing 17, as illustrated in FIGf3B, to hold against upwardly acting force. Thereafter, the cover tube is slowly pulled from about the bridge plug assembly 27. The force required, as indicated hereinbefore, is about 100 pounds and can be easily seen on the weight indicator at the surface. The cover tube and dog release assembly 29 are brought to the surface and removed from the wireline. As the cover tube 31 is pulled from around the packer 103, including both upper and lower packers 105 and 107, it expands radially outwardly into contact with the casing 17, as illustrated in FIG. 4C. Also, the secondary dogs 187 spring outwardly to set against the casing 17 and retain the bridge plug assembly 27 in place against downwardly acting forces. Thus, the combination of the primary dogs 33 and the dogs 187 retains the bridge plug assembly 27 in place against both upward and downward forces,

Also, as indicated hereinbefore, the centralizers 83 will spring outwardly to centralize the vent tube and allow substantially uniform expansion of the packer 103 radially outwardly into contact with the casing 17.

The vent tube 95, in combination with its upper and lower apertures 97 and 99, provides open passageway to allow fluid to flow past the packer 103. Moreover, the lower packer 107 directs and guides the fluid into the lower apertures 97 such that sand or cement slurry can be poured onto the upper packer without danger of being blown therefrom by flow of fluid therepast.

At the surface, the required dump bailer sections are assembled for a sand dump run if sand is to be employed. A base, or short column, of sand on the top packer effects more nearly universally perfect results for some reason. The reason is not exactly clear, but it may be that minor shifts in the respective leaves of the top packer are compensated for by shifting sand grain particles and do not transmit stress to the curing cement slurry that is emplaced thereover. In any event, the bailer is connected with the wireline for making the sand dump run. A predetermined quantity of sand is employed. For example, the predetermined quantity of sand may be enough to set a depth of sand of from six to eighteen inches in the casing. We have found that twelve inches of sand affords an excellent thickness of sand cushion 211, FIG. 5, immediately adjacent the upper packer 105.

The sand dump bailer is lowered to a position about 20 feet above the height of the retrieving knob 133 and the sand dumped. The sand will settle into the upper packer 105. The sand dump bailer is brought to the surface and is prepared for delivering cement slurry.

If possible, additional dump bailer sections should be added for cement runs, since a greater length column of cement is desired, ordinarily, than the column of sand. The dump bailer is lowered to near the sand 211 but no closer than about three feet in order to ensure that the dump bailer does not touch the packers. Otherwise, the packers could be damaged so that they would not seal or hold cement. The cement is dumped onto the sand to a height of about one foot below the top apertures 99 of the vent tube 95., In accordance with conventional practice, the cement is dumped from the dump bailer by firing a squib release of the dump bailer and waiting five to ten minutes for the cement to run out. If a weight loss is indicated before the dump bailer has been lowered to the proper depth, it should be picked up and the lowering procedure repeated, since there is a possibility that the bailer will seat on the centralizer arms instead of passing them. As a result, a column of cement slurry 213, FIG. 6, will be formed on top of the sand column 211. The dump bailer is brought to the surface.

The plug of cement slurry 213 is allowed to cure for 18 hours or more before the open passageway through 1 l the vent tube 95 and the top and bottom apertures 99 and 97 is closed. When set, the cement holds the vent tube 95 via recesses 217, FIG. 5.

When it is decided to move the vent plug 155 into the vent tube 95 below the top apertures 99 to close the open passageway, a suitable retrieving tool is connected to the wireline, preferably below a collar casing locator and a minimum of 75 pounds of sinker bars.

The retrieving tool may comprise a retrieving tool, per se; a fishing tool with collet fingers for grasping the retrieving knob 133; or any other suitable means. A suitable retrieving tool comprises flaring spring fingers and a cover tube. Thus, the spring fingers may be lowered within a cover tube and released just above the retrieving knob. They are then lowered around the retrieving knob and pulled within the cover tube so as to grasp the retrieving knob and hence, the closure rod 128.

Ordinarily, it is advantageous to lower the retrieving tool to plug setting depth and tag the top of the cement in order that this may be accurately recorded in the well data sheets.

The retrieving tool is then pulled up three feet above the retrieving knob and opened; for example, as by firing an explosive stud assembly as described hereinbefore with respect to the dog release assembly. The retrieving tool is lowered until a weight loss is indicated. The retrieving tool should now be latched onto the retrieving knob. Slack is taken up in the wireline and the tattle-tail, in the form of the closure rod 128 and shaft portion 89, is pulled to effect closure of the vent valve. The pull off force is approximately 500-800 pounds. Expressed otherwise, approximately 500-800 pounds pressure is necessary to pull the poppet valve 149 from the aperture, seat and seal 151 and allow well pressure to move the vent plug 155 downwardly into its sealing position. In the illustrated embodiment, the well pressure causes the vent plug 155 to travel about 2% inches. As can be seen in FIGS. 2A, 7 and 8, the well head pressure enters through the aperture, seat and seal 151 to act on piston 161 and force it downwardly, thereby pushing the vent plug 155 downwardly past the top apertures 99 and sealing off the passageway through the vent tube 95. As described hereinbefore, the chucks 179 snap into position to lock the vent plug 155 into place.

If the vent plug 155 does not travel the required distance, about a 1,200 pound pull will be required to break the end off the tattle-tail just above lower shoulders 157 and release the knob 133, retrieving sub 79 and shaft portion 89. Such an abbreviated tattle-tail indicates that corrective action may need to be taken, as will be described later hereinafter.

The well pressure gives a very large force; for example, 2,400 pounds at 5,000 pounds per square inch; to close the vent plug. Closure of the vent plug has been functionally tested at 17,000 psi for good closing characteristics. Also, it will close proper with as little as 50 Usually, only one try is necessary to latch onto the retrieving knob 133. However, if the pull off force was not noted, a second try may be thought necessary. In this case, pull up about feet and repeat the lowering procedure. If the pull off force is not observed, pull up about 5 feet and repeat the lowering procedure until the force is noted.

The retrieving tool and the tattle-tail are brought to the surface. The tattle-tail is removed from the retrieving tool. It will be recalled that the tattle-tail comprises both the closure rod 128 and the shaft portion 89 with the poppet valve 149 at the bottom end.

The ensure that the bridge plug seals completely and for long duration, as is required for permanent type bridge plugs, an additional cement slurry is dumped on top of the cement in column 213. The additional cement slurry is preferably dumped by way of suitable dump bailers, in accordance with conventional practice as delineated hereinbefore. The cement may be emplaced for the desired distance up hole, from a few feet to several tens of feet or more. In any event, it covers the packer and the vent tube assembly 30, since there is no longer any fluid flowing upwardly through the plugged vent tube 95. Any desired strength can be obtained in the resulting final bridge plug, depending upon the length of the cement plug finally effected. There is no problem with the weight of the additional cement slurry, since the column of cement 213, as well as the dog assembly 185, have more than adequate strength to bear the weight for properly engineered bridge plug.

In the foregoing descriptive matter, the following generic considerations are inherent. It will be recalled that the vent plug 155 requires a setting force to move it into its closed position. A means for effecting the setting force is afforded by the poppet valve 149 in the pressure inlet, or aperture, seat and seal 151; the well pressure acting against the piston 161 in the atmospheric chamber 163. Expressed otherwise, a closure means in the form of the piston 16] and the atmospheric chamber 163 acts to effect closure of the vent plug 155 by way of plug shaft 159. The closure means is, in turn, actuated by an actuator means comprising the retrieving knob 133, closure rod 128, shaft portion 89, poppet valve 149 and the pressure aperture, seat and seal 151.

A tattle-tail release means in the form of the balls 139 in the apertures 141 and trapped intermediate the recessed portion 145 on the shaft portion 89 and the skirt 147 release the shaft portion 89 only after the closure means operates properly.

As implicit hereinbefore, suitable sealing surfaces are provided adjacent the longitudinal extent of the traverse of the respective sealing means, or O-rings, to provide the requisite seals and sealing surfaces.

From the foregoing, it can be seen that this invention achieves all of the objects delineated hereinbefore. Specifically, the apparatus 11 can be designed to go through any diameter tubing and set a bridge plug in almost any casing; for example, ranging in sizes from 4 inches to 9 inches and with deviations up to 45. In fact, a series of through-tubing bridge plugs for insertion through 1 inch tubing has been developed. Even larger or smaller size casing and greater deviations can be accommodated. The bridge plug can be set in wells having temperatures in the range of from 60400F and even these limits can be exceeded with adequate precaution. Cement may be set and the vent pipe manually closed at the operators convenience, following setting of the cement; eliminating predetermined time brackets required in the prior art. This through-tubing bridge plug allows setting a bridge plug while a well is producing at rates of 350 barrels a day or greater. This is primarily because the vent plug is not used to carry cement, but is used only for fluid bypass purposes.

In particular, this invention provides the features delineated hereinbefore and not heretofore provided. Specifically, this invention provides a vent plug that can be closed by well pressure; that is locked into its closed position by chucks that are immobilized. The plug at the top portion of the vent tube above the upper vent apertures allows the vent tube to have a larger inside diameter; cement will have less tendency to settle onto the valve; and the tattle-tail is simpler to connect. As will be recalled, the tattle-tail can be brought back to surface to afford positive evidence that a proper seal has been attained with a properly set vent plug 155 in the vent tube 95.

Moreover, the invention provides packers that have both upward and downwardly looking packers. The upper packer serves more effectively to catch and hold the sand, (if employed) and cement slurry. The downward packer serves to channel the fluid flow through the vent tube more effectively. In specific structural features, the packer leaves are designed to provide a tangential opening force that operates satisfactorily even in large diameter casing. The nonwaterproof bag effects a set cement of improved physical characteristics.

A protective steel cover tube is employed during running in to prevent damaging the respective components of the bridge plug assembly 27.

The usual materials of construction may be employed in this invention and no exotic new and expensive materials are required.

Although this invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of this invention.

What is claimed is:

1. A method of emplacing a bridge plug in a wellbore penetrating subterranean formation, said wellbore having casing and tubing therein, comprising the steps of:

a. running a packer assembly containing a covered and collapsed packer and locking dogs downwardly through the tubing to a predetermined depth in said casing in said wellbore;

b. releasing a first set of dogs that engage said casing for holding against an upward force;

c. lifting the cover upwardly from around and expanding said packer and a second set of dogs that engage said casing for holding against a downward force and removing said cover from said wellbore; said packer expanding outwardly into contact with said casing with sufficient force and disposition so as to sustain a cement slurry dumped thereonto;

d. providing an open passageway through said packer to allow fluids to flow through said passageway during curing of any cement slurry dumped onto said packer;

e. removing apparatus including a dog release assembly and a cover tube from said wellbore;

f. dumping a predetermined batch of cement slurry on top of said expanded packer and allowing said cement slurry to set up and partially cure;

g. providing an open passageway through said cement slurry such that said passageway communicates and is maintained open to fluid flow during curing of said cement slurry to set cement;

h. closing said open passageway and pulling from said wellbore a tattle-tail demonstrating that said open passageway has been satisfactorily closed; and

i. thereafter dumping additional cement slurry on top of said cement and said closed passageway and allowing it to set forming a complete bridge plug without requiring removal of said tubing.

2. The method of claim 1 wherein a predetermined amount of said is dumped onto the top of said expanded packer before said cement slurry is dumped thereonto.

3. The method of claim 1 wherein water is allowed to seep from said cement slurry through water-permeable walls of a bag around said expansible packer for effecting cement of improved physical properties.

4. Apparatus for emplacing a bridge plug in a wellbore penetrating subterranean formations, said wellbore having casing and tubing therein, comprising:

a. a cable for running into said wellbore;

b. a collapsed packer for receiving a cement slurry; said packer being suspended from said cable during run-in and being extensible radially outwardly into contact with said casing;

c. a vent tube having upper and lower vent apertures and providing an open passageway through said packer for bypassing fluid during curing of a cement slurry in said packer after said packer has been extended outwardly into contact with said casing and had said cement slurry dumped thereonto;

. vent plug carried by said vent tube and movable to a closed position for plugging said vent tube when said vent plug is subjected to a seating force;

e. lock means for locking said vent plug into its closed position when moved thereinto; said lock means being connected with said vent tube and said packer;

f. closure means for effecting said seating force for moving said vent plug into its closed position; said closure means being connected with said vent plug;

g. actuator means for actuating said closure means;

said actuator means having a portion that is disposed intermediate and adapted to establish fluid communication between said closure means and said wellbore;

h. dog means connected with said vent tube for engaging said casing to hold said vent tube and said packer in place against respective forces upwardly and downwardly; said dog means being connected with said packer and said vent tube;

cover tube covering said packer, said vent tube and said vent plug in a run-in configuration for being run into said wellbore; said cover tube having an outside diameter less than the internal diameter of said tubing so as to move longitudinally therefore; and j. dog release means adapted to release said dog means for engaging said casing to hold against a first upward force sufficient to move said cover tube from around said packer and said vent tube; said release means being operable by an operator at the surface.

5. The apparatus of claim 4 wherein said dog release means comprises a releasable stud; a compressed spring means; a shaft and thrust tube holding said spring means compressed as long as said stud retains said shaft; and means for releasing said stud to allow said spring to kick said shaft and said thrust tube downwardly; and, consequently, said dog means out of the bottom of said cover tube.

6. The apparatus of claim 4 wherein said vent plug is located at the top portion of said vent tube above the upper vent apertures to allow said vent tube to have a larger inside diameter 7. The apparatus of claim 4 wherein said closure means comprises a chamber at a reduced pressure and a piston disposed therewithin and having its upper side in fluid communication with said actuator means so it may be subjected to wellbore fluid pressure; said piston being connected with said vent plug so as to move it to its closed position when said piston is subjected to wellbore pressure.

8. The apparatus of claim 7 wherein said actuator means comprises a well pressure inlet aperture; a poppet valve and sealing seat for blocking said well pressure inlet aperture against flow of fluid therethrough; said poppet valve being connected with a shaft portion of said actuator means and being movable into an open position to cause application of well fluid pressure to the one side of said piston of said closure means for generating said sealing force and moving said vent plug to its closed position.

9. The appartus of claim 7 wherein said apparatus also includes a tattle-tail release means connected with said actuator means and adjacent said closure means such that said shaft portion of said actuator means is released only after said closure means operates properly; and a tattle-tail connected with said shaft portion of said actuator means such that said tattle-tail can be brought to the surface completely intact only if released by said tattle-tail release means; wherein said tattle-tail release means comprises an immobilized sleeve with apertures; a recessed portion on said shaft portion of said actuator means; ball means disposed in said apertures about said recessed portion so said recessed portion can slide with respect to said balls but said balls will not be released until they are able to be moved radially outwardly through said apertures; and a skirt disposed about said sleeve and connected with said piston of said closure means so as to move downwardly with said piston when subjected to said well pressure such that said apertures are opened and said balls can move radially outwardly to free said shaft portion.

10. The apparatus of claim 7 wherein said lock means comprises a plurality of expanded chucks; biasing means tending to force said chucks radially inwardly; and wherein said piston comprises an annular recess for receiving said chucks when moved adjacent; said chucks being fixed longitudinally with respect to said vent tube such that when moved radially inwardly into said recess, said piston is immobilized against longitudinal movement with respect to said vent tube and said packer.

11. The apparatus of claim 4 wherein said packer comprises a pair of packers that, in their extended position, comprise pseudo-frusto-conically shaped packers, one opening upwardly for receiving sand and cement and one opening downwardly for directing fluid flow through said vent tube.

12. The apparatus of claim 11 wherein said packers comprise a plurality of inner radially and peripherally extensible fan-shaped leaves connected to said vent tube near their small end and a bag disposed over said leaves so as to expand therewith.

13. The apparatus of claim 12 wherein each said leaf of said packer contains a spring member that is connected to said vent tube at one end and biased radially outwardly at the other end and a fan-shaped piece attached to said spring member, said fan-shaped piece having an arcuate portion extending from the edge opposite said spring member and along the radially outermost portion of the edge; said arcuate portion increasing monotonically in lateral dimensions from a straight line tangent at the beginning of said arcuate portion and substantially aligned with said edge opposite said spring member before said arcuate portion begins, such that said packer operates more effectively and satisfactorily, particularly in large diameter casing.

14. Apparatus for emplacing a bridge plug in a wellbore penetrating subterranean formations, said wellbore having casing and tubing therein, comprising:

a. a cable for running into said wellbore;

b. a collapsed packer for receiving cement slurry for forming a bridge plug; said packer being suspended from said cable during run-in and being extensible radially outwardly into contact with said casing; said packer comprising in its extended position a pseudo-frusto-conically shaped packer opening upwardly for receiving sand and cement;

c. a vent tube providing an open passageway through said packer for bypassing fluid during curing of a cement slurry in said packer after said packer has been extended outwardly into contact with said casing and had said cement slurry dumped thereonto;

(1. vent plug carried by said vent tube and movable to a closed position for plugging said vent tube when said vent plug is subjected to a seating force acting to move said vent plug into its sealingly closed position;

e. means for effecting said seating force for moving said vent plug into its sealingly closed position; said means being connected with said vent plug;

f. lock means for locking said vent plug into its sealingly closed position; said lock means being connected with said vent tube and said vent plug;

g. dog means connected with said vent tube for engaging said casing to hold said vent tube and said packer in place against respective forces upwardly and downwardly;

h. cover the covering said packer, said vent tube, said vent plug and said dog means in a run-in configuration for being run into said wellbore; said cover tube having an outside diameter less than the internal diameter of said tubing so as to move longitudinally thereof; said cover tube holding said dog means retracted in said run-in configuration; and

i. dog release means disposed at least partly within said cover tube and adapted to release said dog means for engaging said casing to hold against a first upward force sufficient to move said cover tube from around said packer and said vent tube; said dog release means being remotely operable by an operator at the surface.

15. The apparatus of claim 14 wherein said packer also includes in its extended position a pseudo-frustoconically shaped packer opening downwardly for directing fluid flow through said vent tube more effectively.

16. The apparatus of claim wherein said packers comprise a plurality of inner radially and peripherally extensible fan-shaped leaves connected tosaid vent tube near their small end and a bag disposed over said leaves so as to expand therewith, yet catch sand, cement particles and the like.

17. The apparatus of claim 16 wherein said bag has walls that are permeable to water so as to allow Water to seep from said cement slurry through sand emplaced immediately adjacent the bag for effecting a better set cement and said bag has a permeability less than that which would allow too much water to seep from said cement and adversely affect the set cement.

18. The apparatus of claim 16 wherein each said leaf of said packer contains a spring member that is connected to said vent tube at one end and biased radially outwardly at the other end and a fan-shaped piece attached to said spring member, said fan-shaped piece having an arcuate portion extending from the edge opposite said spring member and along the radially outermost portion of the edge; said arcuate portion increasing monotonically in lateral dimensions from a straight line tangent at the beginning of said arcuate portion and substantially aligned with said edge opposite said spring member before said arcuate portion begins such that said packer operates more effectively and satisfactorily, particularly in large diameter casing.

19. A through-tubing bridge plug comprising:

a. a vent tube;

b. a collapsible and extensible packer basket carried by said vent tube, said basket being made up of a plurality of leaves; and

c. a bag covering said packer basket; said bag being of loosely fitting sleeve-like configuration and extending over both the interiorly facing surfaces of said leaves and the exteriorly facing surfaces of said leaves so that the bag is expanded by said leaves when they expand.

20. The apparatus of claim 19 wherein said basket, when extended, has a downwardly facing conical or funnel-like configuration.

21. The apparatus of claim 19 wherein said basket, when extended, has an upwardly facing conical or funnel-like configuration.

22. The apparatus of claim 21 wherein said bag is made of a water permeable material.

23. A through-tubing bridge plug comprising:

a. a vent tube;

b. a collapsible and extensible packer basket carried by said vent tube, said basket made up ofa plurality of leaves; said basket, when extended, having an upwardly facing conical or funnel-like configuration and in addition a downwardly facing conical or funnel-like configuration disposed beneath said upwardly facing configuration; and

c. a bag covering said packer basket.

24. The apparatus of claim 23 wherein said bag covers only said downwardly facing configuration.

25. The apparatus of claim 23 wherein at least the portion of said bag covering said upwardly facing configuration is made of a water permeable material. 

1. A method of emplacing a bridge plug in a wellbore penetrating subterranean formation, said wellbore having casing and tubing therein, comprising the steps of: a. running a packer assembly containing a covered and collapsed packer and locking dogs downwardly through the tubing to a predetermined depth in said casing in said wellbore; b. releasing a first set of dogs that engage said casing for holding against an upward force; c. lifting the cover upwardly from around and expanding said packer and a second set of dogs that engage said casing for holding against a downward force and removing said cover from said wellbore; said packer expanding outwardly into contact with said casing with sufficient force and disposition so as to sustain a cement slurry dumped thereonto; d. providing an open passageway through said packer to allow fluids to flow through said passageway during curing of any cement slurry dumped onto said packer; e. removing apparatus including a dog release assembly and a cover tube from said wellbore; f. dumping a predetermined batch of cement slurry on top of said expanded packer and allowing said cement slurry to set up and partially cure; g. providing an open passageway through said cement slurry such that said passageway communicates and is maintained open to fluid flow during curing of said cement slurry to set cement; h. closing said open passageway and pulling from said wellbore a tattle-tail demonstrating that said open passageway has been satisfactorily closed; and i. thereafter dumping additional cement slurry on top of said cement and said closed passageway and allowing it to set forming a complete bridge plug without requiring removal of said tubing.
 2. The method of claim 1 wherein a predetermined amount of said is dumped onto the top of said expanded packer before said cement slurry is dumped thereonto.
 3. The method of claim 1 wherein water is allowed to seep from said cement slurry through water-permeable walls of a bag around said expansible packer for effecting cement of improved physical properties.
 4. Apparatus for emplacing a bridge plug in a wellbore penetratIng subterranean formations, said wellbore having casing and tubing therein, comprising: a. a cable for running into said wellbore; b. a collapsed packer for receiving a cement slurry; said packer being suspended from said cable during run-in and being extensible radially outwardly into contact with said casing; c. a vent tube having upper and lower vent apertures and providing an open passageway through said packer for bypassing fluid during curing of a cement slurry in said packer after said packer has been extended outwardly into contact with said casing and had said cement slurry dumped thereonto; d. vent plug carried by said vent tube and movable to a closed position for plugging said vent tube when said vent plug is subjected to a seating force; e. lock means for locking said vent plug into its closed position when moved thereinto; said lock means being connected with said vent tube and said packer; f. closure means for effecting said seating force for moving said vent plug into its closed position; said closure means being connected with said vent plug; g. actuator means for actuating said closure means; said actuator means having a portion that is disposed intermediate and adapted to establish fluid communication between said closure means and said wellbore; h. dog means connected with said vent tube for engaging said casing to hold said vent tube and said packer in place against respective forces upwardly and downwardly; said dog means being connected with said packer and said vent tube; i. cover tube covering said packer, said vent tube and said vent plug in a run-in configuration for being run into said wellbore; said cover tube having an outside diameter less than the internal diameter of said tubing so as to move longitudinally therefore; and j. dog release means adapted to release said dog means for engaging said casing to hold against a first upward force sufficient to move said cover tube from around said packer and said vent tube; said release means being operable by an operator at the surface.
 5. The apparatus of claim 4 wherein said dog release means comprises a releasable stud; a compressed spring means; a shaft and thrust tube holding said spring means compressed as long as said stud retains said shaft; and means for releasing said stud to allow said spring to kick said shaft and said thrust tube downwardly; and, consequently, said dog means out of the bottom of said cover tube.
 6. The apparatus of claim 4 wherein said vent plug is located at the top portion of said vent tube above the upper vent apertures to allow said vent tube to have a larger inside diameter
 7. The apparatus of claim 4 wherein said closure means comprises a chamber at a reduced pressure and a piston disposed therewithin and having its upper side in fluid communication with said actuator means so it may be subjected to wellbore fluid pressure; said piston being connected with said vent plug so as to move it to its closed position when said piston is subjected to wellbore pressure.
 8. The apparatus of claim 7 wherein said actuator means comprises a well pressure inlet aperture; a poppet valve and sealing seat for blocking said well pressure inlet aperture against flow of fluid therethrough; said poppet valve being connected with a shaft portion of said actuator means and being movable into an open position to cause application of well fluid pressure to the one side of said piston of said closure means for generating said sealing force and moving said vent plug to its closed position.
 9. The appartus of claim 7 wherein said apparatus also includes a tattle-tail release means connected with said actuator means and adjacent said closure means such that said shaft portion of said actuator means is released only after said closure means operates properly; and a tattle-tail connected with said shaft portion of said actuator means such that said tattle-tail can be brought to the surface completely intact only if released by said tattle-tail release means; wherein said tattle-tail release means comprises an immobilized sleeve with apertures; a recessed portion on said shaft portion of said actuator means; ball means disposed in said apertures about said recessed portion so said recessed portion can slide with respect to said balls but said balls will not be released until they are able to be moved radially outwardly through said apertures; and a skirt disposed about said sleeve and connected with said piston of said closure means so as to move downwardly with said piston when subjected to said well pressure such that said apertures are opened and said balls can move radially outwardly to free said shaft portion.
 10. The apparatus of claim 7 wherein said lock means comprises a plurality of expanded chucks; biasing means tending to force said chucks radially inwardly; and wherein said piston comprises an annular recess for receiving said chucks when moved adjacent; said chucks being fixed longitudinally with respect to said vent tube such that when moved radially inwardly into said recess, said piston is immobilized against longitudinal movement with respect to said vent tube and said packer.
 11. The apparatus of claim 4 wherein said packer comprises a pair of packers that, in their extended position, comprise pseudo-frusto-conically shaped packers, one opening upwardly for receiving sand and cement and one opening downwardly for directing fluid flow through said vent tube.
 12. The apparatus of claim 11 wherein said packers comprise a plurality of inner radially and peripherally extensible fan-shaped leaves connected to said vent tube near their small end and a bag disposed over said leaves so as to expand therewith.
 13. The apparatus of claim 12 wherein each said leaf of said packer contains a spring member that is connected to said vent tube at one end and biased radially outwardly at the other end and a fan-shaped piece attached to said spring member, said fan-shaped piece having an arcuate portion extending from the edge opposite said spring member and along the radially outermost portion of the edge; said arcuate portion increasing monotonically in lateral dimensions from a straight line tangent at the beginning of said arcuate portion and substantially aligned with said edge opposite said spring member before said arcuate portion begins, such that said packer operates more effectively and satisfactorily, particularly in large diameter casing.
 14. Apparatus for emplacing a bridge plug in a wellbore penetrating subterranean formations, said wellbore having casing and tubing therein, comprising: a. a cable for running into said wellbore; b. a collapsed packer for receiving cement slurry for forming a bridge plug; said packer being suspended from said cable during run-in and being extensible radially outwardly into contact with said casing; said packer comprising in its extended position a pseudo-frusto-conically shaped packer opening upwardly for receiving sand and cement; c. a vent tube providing an open passageway through said packer for bypassing fluid during curing of a cement slurry in said packer after said packer has been extended outwardly into contact with said casing and had said cement slurry dumped thereonto; d. vent plug carried by said vent tube and movable to a closed position for plugging said vent tube when said vent plug is subjected to a seating force acting to move said vent plug into its sealingly closed position; e. means for effecting said seating force for moving said vent plug into its sealingly closed position; said means being connected with said vent plug; f. lock means for locking said vent plug into its sealingly closed position; said lock means being connected with said vent tube and said vent plug; g. dog means connected with said vent tube for engaging said casing to hold said vent tube and said packer in place against respective forces upwardly and downwardly; h. cover the covering said packer, saId vent tube, said vent plug and said dog means in a run-in configuration for being run into said wellbore; said cover tube having an outside diameter less than the internal diameter of said tubing so as to move longitudinally thereof; said cover tube holding said dog means retracted in said run-in configuration; and i. dog release means disposed at least partly within said cover tube and adapted to release said dog means for engaging said casing to hold against a first upward force sufficient to move said cover tube from around said packer and said vent tube; said dog release means being remotely operable by an operator at the surface.
 15. The apparatus of claim 14 wherein said packer also includes in its extended position a pseudo-frusto-conically shaped packer opening downwardly for directing fluid flow through said vent tube more effectively.
 16. The apparatus of claim 15 wherein said packers comprise a plurality of inner radially and peripherally extensible fan-shaped leaves connected to said vent tube near their small end and a bag disposed over said leaves so as to expand therewith, yet catch sand, cement particles and the like.
 17. The apparatus of claim 16 wherein said bag has walls that are permeable to water so as to allow water to seep from said cement slurry through sand emplaced immediately adjacent the bag for effecting a better set cement and said bag has a permeability less than that which would allow too much water to seep from said cement and adversely affect the set cement.
 18. The apparatus of claim 16 wherein each said leaf of said packer contains a spring member that is connected to said vent tube at one end and biased radially outwardly at the other end and a fan-shaped piece attached to said spring member, said fan-shaped piece having an arcuate portion extending from the edge opposite said spring member and along the radially outermost portion of the edge; said arcuate portion increasing monotonically in lateral dimensions from a straight line tangent at the beginning of said arcuate portion and substantially aligned with said edge opposite said spring member before said arcuate portion begins such that said packer operates more effectively and satisfactorily, particularly in large diameter casing.
 19. A through-tubing bridge plug comprising: a. a vent tube; b. a collapsible and extensible packer basket carried by said vent tube, said basket being made up of a plurality of leaves; and c. a bag covering said packer basket; said bag being of loosely fitting sleeve-like configuration and extending over both the interiorly facing surfaces of said leaves and the exteriorly facing surfaces of said leaves so that the bag is expanded by said leaves when they expand.
 20. The apparatus of claim 19 wherein said basket, when extended, has a downwardly facing conical or funnel-like configuration.
 21. The apparatus of claim 19 wherein said basket, when extended, has an upwardly facing conical or funnel-like configuration.
 22. The apparatus of claim 21 wherein said bag is made of a water permeable material.
 23. A through-tubing bridge plug comprising: a. a vent tube; b. a collapsible and extensible packer basket carried by said vent tube, said basket made up of a plurality of leaves; said basket, when extended, having an upwardly facing conical or funnel-like configuration and in addition a downwardly facing conical or funnel-like configuration disposed beneath said upwardly facing configuration; and c. a bag covering said packer basket.
 24. The apparatus of claim 23 wherein said bag covers only said downwardly facing configuration.
 25. The apparatus of claim 23 wherein at least the portion of said bag covering said upwardly facing configuration is made of a water permeable material. 